Toyota Camry P0174: Meaning, Causes, How to Fix

One of the most common trouble codes with the Toyota Camry is P0174. It indicates that your Toyota Camry is running lean on the bank two side of the engine. 

P0174 and P0171 (fuel trim lean bank one) are the most frequently seen air/fuel mixture-related codes. If they appear together, it reduces the list of potential causes (more on that in the last section of the article.

The most common causes of P0174 are a vacuum leak or a dirty MAF sensor.

Toyota Camry P0174

DefinitionP0174: Fuel Trim System Lean (Bank 2).
SymptomsCheck engine light, decreased fuel economy, misfire, hard to find idle.
Common CausesDirty MAF sensor, vacuum leak, O2 sensor.
Breakdown Risk?Rarely.
Repair Cost (Parts)It varies, but the most common repairs are usually under $200.
Repair DifficultyThe common P0174 repairs are usually simple.

Table of Contents

P0174 Definition: Fuel Trim System – Lean (Bank 2)

P0174 is a generic code, so it has the same meaning for the Toyota Camry as any other vehicle.m Here’s all three parts of the definition, divided by its three parts:

Fuel Trim System

The ideal air/fuel ratio is 14.7:1 (14.7 parts air to one part fuel).  Your Camry’s PCM will try and stay as close to this number as possible (it can range anywhere from 12.0:1 for power and 16.0:1 for economy).

Here are the main components of the fuel trim system.

  • O2 sensors– Oxygen sensors meter the exhaust and report the oxygen content to the powertrain control module.
  • MAF or MAP sensor– Depending on your Camry’s model year, it can have a mass airflow sensor or manifold absolute pressure sensor (or both).  Their job is to meter the air as it enters the engine.
  • Powertrain control module– Takes info from these sensors and uses it to adjust the air/fuel ratio.

There’s more to how your Camry gets air and fuel than what’s listed above, but these are the big three components that meter and adjust the fuel trim.

System Lean

P0174 is thrown when your carotruck’s B2S1 O2 sensor detects the air-fuel mixture is “lean” (too much air or not enough fuel).

Your Camry’s PCM will add more fuel to the mixture to bring the air-fuel mixture where it needs to be for optimal combustion. It also throws the code P0174 to let you know it has done this. Most of the time, there won’t be any noticeable drivability issues.

Bank 2

Bank two is the side of your Toyota Camry’s engine with the second cylinder. For most engines, that’s the cylinder head a little further from the engine accessories.

If your car has P0171 + P0174, it indicates the entire engine is running lean, so you don’t really need to concern yourself over finding bank 2.

Toyota Camry P0174: Symptoms

P0174 Symptoms

There aren’t usually any drivability issues associated with P0174. Typically, the first sign that anything is wrong is the check engine light.

  • Mileage- may or may not suffer depending on how much the air-fuel mixture has changed.
  • Misfire– If the air-fuel mixture has gotten too far from the 14.7:1 sweet spot, this can cause your Toyota Camry to misfire.
  • Idle Issues– With the air/fuel mixture altered, the vehicle can idle erratically as the computer compensates to keep the engine running.

Causes of P0174 in the Toyota Camry

The P0174 code is thrown when something has caused too much air to get into your Camry’s combustion chamber or the fuel pressure at the rail is below where it needs to be.

Vacuum Leaks

Your Camry’s MAF and/or MAP sensors meter the air as it enters the engine.  If there is an air leak after the MAF sensor, it’s not being measured as it enters the intake, which increases the air in the air-to-fuel ratio.

One of the most common causes for the P0174 code to show is a vacuum leak.  Listen and look around your Toyota Camry’s engine bay to see if you can find the vacuum leak. 

Look at any hoses or sensors that connect to the intake manifold.  Verify that they aren’t cracked and that they are tightly secured.  Listen for unusual noises.

Oxygen Sensor

The P0174 code is thrown when the bank two sensor one O2 sensor reports that your Camry’s engine is running lean.  

Swap Test

If your Camry has P0174 without P0171 present, you can swap the bank one and two O2 sensors and see if the code “jumps” to the other bank. Here’s what you do.

  1. Clear the diagnostic trouble codes with your scanner.
  2. Swap the bank one sensor one oxygen sensor with its bank two counterpart.
  3. Start your Camry and wait for the check engine light to come back on.
  4. Once you pull the codes, if it changes to P0171, that’s enough evidence that a faulty O2 sensor was causing P0174 in your car.

Mass Air Flow (MAF) Sensor

Bad MAF P0174
Here are a couple of common MAF sensor styles

The mass air flow sensor calculates the volume of air entering the engine. If it is malfunctioning, your car’s PCM won’t know how much air is entering the engine.  When this happens, it can cause your Toyota Camry’s engine to run rich or lean.  If it were running rich, you’d get P0175.

Cleaning the MAF or MAP Sensor

Your Camry’s MAF sensor is covered with tiny electrodes that can detect how much air is passing through it. Unfortunately, it can’t read the air properly if it gets dirty.

Local parts stores sell dedicated MAF sensor cleaners.  If you use anything else to clean it, you risk damaging its sensitive electronics.

Fuel Injectors

Fuel Injectors can Cause P0174

P0174 indicates that your Toyota Camry is either getting too much air or not enough fuel. A clogged or damaged fuel injector will cause the air-fuel mixture to lean out in one specific cylinder.  You may see a cylinder misfire code or fuel injector-specific code with P0174.

It’s unlikely that you’ll see P0171 if this is the case. You may also get P0300 or P030X (X being the missing cylinder, which should be an even number).

Fuel Pressure Regulator or Fuel Pump

Typical Fuel Pump

With P0174, there’s possibly not enough gas entering the combustion chambers.  This can happen if the fuel pressure regulator isn’t allowing enough fuel to get to the fuel rail.

A faulty fuel pump behaves exactly the same way. The only way to know why the fuel pressure is too low and causing P0174 in your Toyota Camry is to trace it back from the fuel rail and see where the pressure starts weakening.

Exhaust Leak

An exhaust leak will change the amount of oxygen the B2S1 O2 sensor picks up.  When this happens, it’ll report a false lean condition.  You’ll likely hear the exhaust leak coming from under the front of your Camry.

Air Filter

While it’s not the most common reason to throw the P0174 code, a clogged air filter can cause it. It only takes a second to check it.

Possible P0174 Fixes

Toyota Camry P0174 Diagnosis

Here are the steps you can take to diagnose P0174 in the Toyota Camry.

  1. Check for other trouble codes. They will likely point you to what part of your car is malfunctioning.
  2. Listen for an exhaust leak or vacuum leak within the engine. The exhaust leak should be close to the B2S1 O2 sensor.
  3. Inspect all of the hoses that connect to the intake manifold, as well as the intake hose in front of the throttle body.
  4. Check to see if the air filter is dirty.
  5. Test to see if the intake manifold gasket has a leak.
  6. Test the fuel pressure. Some vehicles will tell you how hard the fuel pump is working on a scanner.
  7. Verify fuel trim on a quality scanner.

Common Questions

Is P0174 a breakdown risk?

It is rare that a vehicle breaks down by itself when P0174 is the only code. Still, you don’t want to ignore it. Doing so may eventually damage your Camry’s catalytic converter.

My Camry has P0174 and P0171 together; what does that mean?

If your Toyota Camry has P0174 and P0171 together, it rules out a few problems and provides anecdotal evidence to help narrow the problem.

  • Your Camry’s O2 sensors are likely working fine since they are both reporting the car is running lean.
  • One bad fuel injector will not make a lean code appear on BOTH sides of the engine, so you can rule those out.
  • It’s unlikely there’s an exhaust leak.
  • It leaves the MAF (or MAP) sensor, vacuum leak, air filter, or fuel pressure on the table as possible causes since they would equally affect both sides of your Camry’s engine.

Is P0174 difficult to repair?

P0174 in the Toyota Camry is not difficult to repair. On the other hand, it is difficult to diagnose. Looking up any other codes that appeared with it can save time.